SoylentNews is people
SoylentNews
Could we harness energy from black holes?:
A remarkable prediction of Einstein's theory of general relativity -- the theory that connects space, time and gravity -- is that rotating black holes have enormous amounts of energy available to be tapped.
[...] [Now] physicists Luca Comisso of Columbia University and Felipe Asenjo of the Universidad Adolfo Ibáñez in Chile have found a new way to extract energy from black holes by breaking and rejoining magnetic field lines near the event horizon, the point at which nothing, not even light, can escape a black hole's gravitational pull.
"Black holes are commonly surrounded by a hot 'soup' of plasma particles that carry a magnetic field," said Comisso. "Our theory shows that when magnetic field lines disconnect and reconnect in just the right way, they can accelerate plasma particles to negative energies, and large amounts of black hole energy can be extracted."
The U.S. National Science Foundation-funded research results could allow astronomers to better estimate the spin of black holes and possibly discover a source of energy for the needs of an advanced civilization, Comisso said.
[...] "Thousands or millions of years from now, humanity might be able to survive around a black hole without harnessing energy from stars," Comisso said. "It is essentially a technological problem. If we look at the physics, there is nothing that prevents it."
Journal Reference:
Luca Comisso, Felipe A. Asenjo. Magnetic reconnection as a mechanism for energy extraction from rotating black holes, Physical Review D (DOI: 10.1103/PhysRevD.103.023014)
(Score: 2) by takyon on Sunday January 24 2021, @01:37PM (13 children)
I think it's possible to approach a black hole if it's supermassive and doesn't have a death trap of hot plasma moving around at light speed near it.
How to harness gravitational energy from a real life black hole? That's somebody else's problem.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2, Funny) by The Mighty Buzzard on Sunday January 24 2021, @02:03PM
It's Hole of Color, you insensitive clod!
My rights don't end where your fear begins.
(Score: 4, Informative) by Immerman on Sunday January 24 2021, @02:23PM (11 children)
As I recall, the more massive the black hole, the lower the tidal forces as you approach the event horizon - sufficiently massive and you could actually cross the event horizon without being torn apart by tidal forces. The loss of any outflowing causal connections would presumably dissolve you anyway, but hey, at least you wouldn't be spaghettified.
If you're just looking to get close though, in many ways smaller is better - e.g. if you magically compressed Phobos into a black hole, the event horizon would be miniscule, and from a couple dozen meters away it'd provide gravity comparable to Earth's with less tidal weirdness than a modest-sized rotating space station. If you were orbitting so that only tidal forces are an issue, you could get within a few meters without too much discomfort, and equipment with a small radial size could get within a few hands without needing anything fancy to resist the tidal forces. If you're playing with the interaction of force-fields, that's probably plenty close enough. Though with such a small event horizon you might not be able to exploit much.
(Score: 3, Interesting) by stormwyrm on Sunday January 24 2021, @02:29PM (8 children)
Numquam ponenda est pluralitas sine necessitate.
(Score: 4, Informative) by Immerman on Sunday January 24 2021, @08:51PM (7 children)
Phobos isn't quite that small, it's still much too much to put out a lot of power. According to https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator [vttoth.com]
a black hole of Phobos' mass (10^16kg) would have an effective
- temperature of 12 million K
- diameter of 30 pm (about 1/3 the diameter of a hydrogen atom, or 36,000x the diameter of a proton)
- total power output (luminosity) of about 3.6W
- and thanks to the low power output, would outlive the stars by many orders of magnitude.
So basically, blazing hot, but with such a tiny surface area that it doesn't actually radiate much power. However, you could potentially use it as the core of a mass-energy converter, feeding it any scrap material as a fuel vastly more energy dense than fusion. Which might actually be more convenient than a radiant black hole, since you would have total control over the power output.
Then again, if you've got the ability to create artificial black micro-holes it's probably far more useful to create something small enough to output a more useful amount of baseline power on its own - at 10^11kg (about 500 cruise ships) it'd be putting out 35GW, and still last for a couple billion years.
(Score: 0) by Anonymous Coward on Monday January 25 2021, @06:57AM (1 child)
so how do you get a hold of a tiny black hole?
I always thought it would be good to give it an electric charge and then you can literally get a handle on it... but it seems like it's a very dangerous thing to have around.
(Score: 2) by Immerman on Monday January 25 2021, @03:01PM
Well, electro-magnetics and gravity are the ONLY forces that act at human scales (physical contact = electrostatic repulsion of electron clouds), so really your only options are giving it an electrostatic charge so you can manipulate it with charges and magnetic fields, or just relying on its mass, tugging it around using an outside mass as a "lure".
Either way, the big danger would be making sure nothing got too close - from an appreciable distance away (say, at the distance where the original surface had been), the gravitational effects will be no different than the original normal mass.
(Score: 2) by Muad'Dave on Monday January 25 2021, @01:01PM (4 children)
I thought tiny black holes evaporated [briankoberlein.com].
(Score: 2) by Immerman on Monday January 25 2021, @02:45PM (3 children)
They do - but the smaller they are, the greater the power output, and thus the faster they lose mass. The tiny ones with atom-scale masses that might be produced at the LHC would evaporate instantly. But Phobos is still pretty massive - at ~10km across it's still a good sized mountain.
Try the calculator, it's fun to play with, just put in the mass and it'll tell you size, lifespan, luminosity(=power output), etc. in whatever units you want https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator [vttoth.com]
Some examples around the tipping point:
Cruise ship (200e6kg): 7e15W, 32y
Olympic-sized swimming pool (2.5e6 kg): 5.7e19W, 22 minutes
40ft shipping container, filled to max (35e3kg): 3e23W, 3ms
Of course, that assumes both that we properly understand Hawking radiation, and that there is no other quantum weirdness that starts messing with black holes smaller than an atom.
(Score: 2) by Immerman on Monday January 25 2021, @03:04PM (2 children)
Oh, and just to put that power output in context:
That cruise ship would be putting out roughly 4x as much power as reaches the entire Earth from the sun.
The shipping container would be putting out almost 1/1000th of the sun's total power.
(Score: 2) by Muad'Dave on Tuesday January 26 2021, @12:32PM (1 child)
Thank you for your informative replies to my questions!
(Score: 2) by Immerman on Tuesday January 26 2021, @02:16PM
You're welcome. You got me curious as to where exactly the tipping point was.
(Score: 2) by Muad'Dave on Monday January 25 2021, @12:41PM (1 child)
Wouldn't its gravity be exactly that of Phobos? Just because it's concentrated doesn't mean it would increase.
(Score: 2) by Immerman on Monday January 25 2021, @03:19PM
At any given distance you would be correct, but gravity acceleration varies with distance from the center of mass according to the inverse square law: g = G*m/r^2
When we talk about the gravity of a planet, we're talking at the surface - a.k.a. the point of maximum gravity. Fly upwards, and you're getting further away, so gravity diminishes. Dig under the surface and gravity starts diminishing again, since you're also getting pulled upwards by the mass above you.
But since a black hole is far tinier than a normal object of the same mass, you can get far closer. Get 10x closer, and gravity gets 100x stronger. For a small black hole you could enclose it in shells of various sizes, and each shell would have a different surface gravity based on its distance. The closer you got, the stronger the pull would be, and also, the stronger the tidal forces: your feet would be closer than your head, and thus be pulled more strongly.